Method and apparatus for filling thermostat tubes with mercury



May 1954 w. M. SMITH ET AL 2,679,343

METHOD AND APPARATUS FOR FILLING THEIRMOSTAT TUBES WITH MERCURY Filed Oct. 6, 1949 2 Sheets-Sheet 1 .13 .14 INVENTORS.

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y 5, 1954 w. M. SMITH ET AL 2,679,343

METHOD AND APPARATUS FOR FILLING THERMOSTAT TUBES WITH MERCURY Filed Oct. 6, 1949 2 Sheets-Sheet 2 l/W, i

Patented May 25, 1954 SATES PATENT OFFICE METHOD AND APPARATUS FOR FILLING THERMOSTAT TUBES WITH MERCURY Application October 6, 1949, Serial No. 119,859

Claims.

This invention relates to an improved method and means for filling mercury column thermostat tubes.

A principal object of the invention is to provide an improved method and means for filling mercury column thermostat tubes, which will embrace the desired features of simplicity, efficiency, rapidity of operation and which will be reliable and convenient in use.

Other objects and advantages of the invention will be apparent during the following description.

An approved form of apparatus embodying the principles of the present invention is shown in the accompanying drawings, wherein:

Figure 1 is an elevational view partly in section and showing an arrangement of apparatus for carrying out the initial steps of the method.

Figure 2 is a similar View showing an arrangement of apparatus for carrying out the final steps of the method.

Referring to the drawings, the numeral 5 designates a vacuum chamber in the nature of a depending well in a table top 6. Preferably, the mouth 1 of the chamber 5 extends slightly above the surface of the table top 6 so as to effect sealing engagement with the mouth of a bell jar 8 when the same is brought into registration therewith, as will be hereinafter described.

Communicating with vacuum chamber 5, through an elbow conduit 9, is a mercury diffusion pump of a known commercial form, which pump is indicated generally by numeral l l. A portion of said pump is provided with cooling coils 12 through which a suitable coolant is circulated and with an electrical heating means disposed in the bottom thereof for vaporizing the mercury in the pump reservoir l3. The said heating means is connected to a source of electrical current through electrical conduit it. Mounted in the elbow conduit 9 is a manually operable needle valve it which opens to the atmosphere. The diffusion pump l is connected to a vacuum conduit l! leading to a vacuum pump (not shown) for producing a vacuum in the conduit ll.

Suitably supported above the vacuum chamber 5 is a closed vessel It containing mercury and communicating with vacuum chamber 5 through conduit l9, the terminal portion of which is arranged to discharge into a receptacle 2|, for example a beaker, contained in the chamber '5, the beaker having a stainless steel screen or perforated plate 22 spaced from the bottom thereof. For illustrative purposes the vessel I8 is here shown as a flask supported on a ring stand 23, the flask being provided with a discharge opening 24 connected to the conduit 59, and a filling opening 26. Heating means, for example a Bunsen burner 27, is adapted to heat the flask 18 to vaporize a portion of the mercury therein. The flask [8, as herein illustrated, is movable to a variety of positions in the ring stand 23 so as to permit either the mercury vapors to pass into the vacuum chamber 5 or the liquid mercury into the receptacle 2|, as will be hereinafter explained.

As shown in Fig. 1, arranged above the vacuum chamber 5 is a heating means, in the form of a plurality of infra-red lamps 23 carried on a suitable support 29, which may be moved out of position to allow positioning of the bell jar 8 in sealing engagement with the vacuum chamber 5, as shown in Fig. 2.

In carrying out the method of our invention the capillary tubes forming the thermostat tube blanks 3i to be filled with mercury, having been previously provided with suitable electrode wires 30-30, are placed in the beaker 2 I, the open ends of said tube blanks facing downwardly and resting on the screen 22, the screenserving to elevate the said blanks from the bottom of the beaker and insures against closing off of the capillary bores during the filling operation. With the lamps 28 in the position as shown in Fig. 1, the chamber 5 as well as the tube blanks 3| are heated by the lamps to approximately 250 F. to dry out any moisture within the chamber and within the bores of the tube blanks. Thereafter, the lamps 28 are removed or swung away to permit positioning of the bell jar 8 in sealing engagement with the chamber 5, as shown in Fig. 2, so as to provide a closed fluid tight system. The vacuum pump is then caused to be operated to evacuate the air from the said system. Commercial vacuum pumps of the type herein employed are effective only to draw a vacuum equal to about 500 microns of mercury. Accordingly, when the pump has reached the limit of its capacity the mercury difiusion pump is caused to be placed in operation. since thestructure and operation of pumps of this type are well known in the art a description of the operation of such a pump is not considered to be necessary. It is known that pumps of this type are capable of drawing a high degree of vacuum giving a pressure of the order of .001 micron of mercury.

Concurrently with the operation of the vacuum pump and the mercury diffusion pump II the flask l8 containing mercury is heated to drive oii any moisture which may be contained therein, since moisture is conducive to the oxidation of mercury and the presence of any oxide in the capillary bore of a thermostat tube interferes with its efficient operation. Also, the liquid mercury in the flask is heated for the purpose of vaporizing the same and the vapor is caused to enter into the chamber through conduit 19. The mercury vapor diffuses throughout the chamber and comingles with any stray air molecules present therein, thereby providing a medium of increased density which may be effectively acted upon by both the vacuum pump and the mercury diifusion pump. Thus, as the mercury vapor is evacuated the stray air molecules are borne along therewith and are simultaneously removed from the chamber and from the capillary tube bores. By the use of this method we have found that a vacuum giving a pressure of the order of 0.5-5 microns of mercury can be attained in about of the time heretofore required for performing similar operations according to prior known methods. We have found that when the degree of vacuum drawn gives a pressure range of 0.5-5 microns of mercury the conditions are ideal for filling the tube blanks, since with a vacuum of a higher pressure than 5 microns difficulties are experienced in metering the tubes, that is to say the removal of surplus mercury from the tubes so that they will function at a predetemined temperature. We therefore consider the range of vacuum indicated as being critical.

When the desired degree of vacuum has been attained the flask I8 is tipped so that the discharge end 24 thereof is below the level of the mercury contained therein and the liquid mercury is caused to flow by gravity through the conduit 19 and into the beaker 2|. When the mercury in the beaker 2! has reached a desired level sufficient of course to submerge the open ends of the tube blanks iii the flow of liquid mercury is arrested by elevating the discharge end of the flask i8. Concurrently the operation of the vacuum pump and mercury diffusion pump 1 l are arrested and the valve i6 is opened to permit air at atmospheric pressure to enter into the system herein described. Since the capillary bores of the tube blanks 3i have been evacuated atmospheric pressure acting on the pool of mercury in the beaker 2i surrounding the open ends of the tube blanks 3| creates a pressure differential which drives the liquid mercury into the capillary bores of the tube blanks to fill the same. Thereafter, the filled tubes are sealed in any suitable manner to prevent oxidation of the mercury. The excess mercury is then removed from the tubes in a well known manner.

It is to be understood that the apparatus herewith shown and described is merely illustrative of one example of suitable means for carrying out the method of our invention and that various changes in type, shape, size and arrangements of parts may be resorted to without departing from the spirit of our invention or the scope of the appended claims.

We claim:

1. An apparatus for filling thermostat tubes with mercury comprising a fluid tight chamber, means for evacuating the air from said chamber and tubes including a mercury diffusion pump and a vacuum conduit connected in series and communicating with said chamber, means for heating said chamber and tubes therein to vaporize all traces of moisture from the Walls thereof, a closed vessel containing liquid mercury and having heating means associated therewith for vaporizing said mercury during the evacuation of said chamber, conduit means connecting said vessel and said chamber for selectively conducting mercury vapor or liquid mercury to said chamber, and valve means to open said chamber to the atmosphere.

2. The method of filling thermostat tubes with mercury which consists in the steps of placing the empty tubes with their open ends inverted into a chamber with the open ends of said tubes extending toward the bottom of the chamber, drying the chamber and the tubes contained therein, evacuating the chamber to attain a pressure of 5 to 0.5 micron While diffusing mercury vapor throughout the chamber, thereafter introducing liquid mercury into the evacuated chamber in a quantity suflicient to provide a pool of a quantity sufficient to fill the tubes and to keep their open ends submerged, and thereafter admitting atmospheric air into the chamber to create a pressure differential as between the interior of the chamber and the interior of said tubes, whereby the liquid mercury is forced from the lower portion of the mercury pool into the tubes to substantially fill them.

3. The method according to claim 2 characterized in that the open ends of the thermostat tubes are spaced slightly above the bottom of the chamber.

4. The method according to claim 3 charactericed in that the mercury is stored in a flask arranged above the vacuum chamber, having open communication with the vacuum chamber and in that heat is applied to the flask to create the mercury vapor diffused throughout the vacuum chamber.

5. An apparatus for filling thermostat tubes as defined in claim 1 characterized in that the closed vessel for containing the liquid mercury is tiltably supported so that it can be arranged in a position to discharge the liquid mercury therefrom.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 449,443 Hall -1 Mar. 31, 1891 845,670 Thomas Feb. 26, 1907 1,345,347 Chaney July 6, 1920 1,862,821 Henderson June 14, 1932 2,178,326 Lecorguillier Oct. 31, 1939 2,311,930 Chirelstein Feb. 23, 1943 2,501,397 Lopez Mar. 21, 1950 

